The present invention relates to a device for preventing a wheel lock of a vehicle, and more particularly, for preventing locking of front and rear wheels of a vehicle of the type in which an engine power is distributed to the front and rear wheels by means of inter axle differential.
There have been proposed examples of such vehicle in which the engine power is distributed to the front and rear wheels by means of the inter axle differential such as disclosed in Japanese Patent Publication No. HEI 5-58933 and Japanese Patent Publication No. HEI 7-53492.
In such vehicles, the power of the engine is distributed to front and rear propeller shafts through a transmission and an inter axle differential (center differential), and the front propeller shaft drives two lateral front wheels and the rear side propeller shaft, on the other hand, drives two lateral rear wheels.
Furthermore, in these vehicles, road ability is achieved by locking the inter axle differential upon detection of slip of the wheels. However, in such vehicles, any attention is not paid at all to an occasion that the rotation of wheels is forcibly stopped (wheel lock state) by being overly braked.
An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide a vehicle wheel lock prevention device capable of preventing the wheel lock of a vehicle by automatically locking an inter axle differential upon detection of the wheel lock state.
This and other objects can be achieved according to the present invention by providing a device for preventing wheel lock of a vehicle in which an engine output power is transmitted to front and rear wheels of the vehicle through a transmission and an inter axle differential, the vehicle wheel lock prevention device comprising:
a differential lock mechanism for locking the inter axle differential;
means for detecting a wheel lock state of the front and rear wheels; and
means for operating the differential lock mechanism so as to lock the inter axle differential by operating the differential lock mechanism upon the detection of the wheel lock state.
According to this aspect, in the case where the wheel lock is detected, inter axle differential is automatically locked, and hence, the wheel lock can be prevented. Therefore, abnormal wearing of the tires of the wheels can be effectively prevented, and moreover, the operability of the retarder brake when the vehicle provided therewith goes down a downhill slope.
In a preferred embodiment of the above aspect, the wheel lock detection means is operated to detect the wheel lock state in a case where a relative revolution number difference between a transmission output revolution number and a differential revolution number in a braking state of brakes of the front and rear wheels is more than a preliminarily set revolution number, the differential lock mechanism operating means is composed of a differential lock valve discharging a pressurized oil to the differential lock mechanism, and the differential lock valve is operated upon the detection of the wheel lock state to thereby discharge the pressurized oil.
According to this structure, the wheel lock condition is detected in comparison of the relative revolution number difference between the transmission output revolution number and the differential revolution number with the preliminarily set revolution number under the braking state of the front and rear wheels. Therefore, the wheel lock state is never detected in the brake released state. Accordingly, since the wheel lock can be surely detected and the inter axle differential is locked, the wheel lock can be surely prevented, and the inter axle differential is never erroneously locked at a time other than the wheel lock time. Further, since the differential lock mechanism is operated by the pressurized oil discharged from the differential lock valve, the differential lock mechanism may be composed of a general type hydraulic clutch.
The wheel lock detection means is provided with a plurality of preliminarily set revolution numbers and operated to generate a wheel lock signal in accordance with the wheel lock state upon the detection of the wheel lock in a case where the relative revolution number difference is more than each of the set revolution numbers stored in the wheel lock detection means, and the differential lock valve discharges the pressurized oil having a pressure in accordance with the detected wheel lock signal to the differential lock mechanism to thereby create a differential lock state in accordance with the wheel lock state.
According to this structure, the differential locking state (degree) of the inter axle differential is made in accordance with the wheel lock state and the wheel lock can be effectively prevented.
The nature and further characteristic features will be made more clear from the following descriptions made with reference to the accompanying drawings.